1, Technical Field
The present invention relates to an optical disk drive, and more particularly, to adjustment of power of a recording laser beam.
2, Related Art
ROPC (running OPC) for detecting the quantity of light reflected from an optical disk during recording of actual data, to thus increase or decrease the power of a recording laser beam in accordance with the quantity of reflected light, has hitherto been put into practice, in conjunction with an OPC technique of recording test data by means of changing the power of the recording laser beam in various manners in a predetermined test area on the optical disk when data are recorded on the optical disk and reproducing the test data, to thus set optimal recording power in accordance with the quality of reproduction.
By means of ROPC, a level B portion—where pits are formed by means of a recording laser beam and where the quantity of light reflected from the pits, among the quantity of light reflected during recording of data, becomes stable—is detected by means of sampling, and the power of a recording laser beam is increased or decreased in accordance with the value of the level B. For instance, given that the power of a recording laser beam is taken as P and the value of the level B is taken as B, the power P of a recording laser beam is adjusted such that B/Pn becomes constant, where “n” is set to, e.g., a value of two or the like.
The level B portion is preferably sampled by means of pits having the longest-possible data length, in consideration of the time required to make the level B portion stable, or in consideration of a filtering range or the like. For instance, in the case of a DVD, the quantity of reflected light is sampled into a data length of 9 T to 11 T, 14 T, and the like, thereby acquiring the value of the level B.
Japanese Patent Laid-Open Publication No. 2002-157738 describes an optical disk drive which rotates, at a constant angular velocity, a disk having, from an inner track to an outer track, a test write area, a buffer area, a lead-in area, a program area, and a lead-out area. The publication describes that a test signal is recorded in an outer peripheral area located outside the test write area and the lead-out area, and that the thus-recorded test signal is reproduced, to thus set the value of a laser output.
By means of ROPC, the level B is detected at a timing when data are recorded into a pit of the longest-possible length. However, the absolute time of a recording pulse becomes shorter in response to a request for increased data recording speed. Even when attention has been paid to a pit of long data length, considerable difficulty is encountered in stably detecting the level B.
When the type of an optical disk is changed, there is also presumed a case where a pit of longer data length is not present. For instance, in a blu-ray disk, which is one type of next-generation optical disk, the maximum data length is 8 T, and even a synchronous signal has a data length of only 9 T, and much greater difficulty is encountered in detecting the level B. There has also been known a “recalling method” comprising the steps of interrupting recording of data during recording operation, evaluating the quality of data recorded immediately before, and adjusting the power of the recording laser beam in accordance with a result of evaluation. When the power of the recording laser beam is adjusted by means of evaluating the quality of the data recorded immediately before and through use of a β value, a γ value, an error rate, it is necessary to know the manner of increasing or decreasing the power of the recording laser beam in relation to an evaluation parameter, such as the β value, the γ value, or the like; namely, it is necessary to accurately ascertain a relationship between the power of the recording laser beam and the evaluation parameter. Such knowledge can be acquired at the test area where OPC is to be performed. The test area where OPC is to be performed and areas where actual data are recorded generally differ from each other in terms of recording sensitivity. Difficulty is encountered in accurately adjusting the power of the recording laser beam.